This invention relates to an image overlay printing controlling method and apparatus for a printer for carrying out image overlay printing in an overlapping relationship with characters or independently.
A printer which is connected to and used with a personal computer or a word processor normally has a function for carrying out image overlay printing on characters in order to attract attention to a portion to be emphasized. Normally, image overlay data are produced by a personal computer or a word processor to which a printer is connected, and the printer carries out image overlay printing in accordance with a command from such apparatus. However, a personal computer or a word processor of a certain type does not have a function of image overlay printing, and when printing is to be carried out by a printer connected to such personal computer or word processor, the lack of an image overlay printing function is inconvenient. Thus, a printer has been proposed which itself has an image overlay printing function.
A printer having an image overlay printing function includes an image overlay data storage section in which image overlay basic data for a predetermined total number of columns are stored, and an image overlay controlling section for controlling image overlay printing. In order to carry out image overlay printing with a printer of the type mentioned, if a number of columns (a start column and an end column) for a print line along which image overlay printing is to be effected is designated, then the image overlay controlling section reads out image overlay basic data by a plurality of times from the image overlay storage section and transfers them to a line buffer until the designated column is reached, and after image overlay data for a required number of columns are obtained in the line buffer, a printing controlling section controls a print head to carry out image overlay printing.
According to such a conventional image overlay printing controlling method as described above, however, since image overlay basic data for a predetermined total number of columns are read out successively beginning with the head position, there is a problem that, if image overlay printing of a designated print line is first carried out and then image overlay printing is started from a different column position for a next print line, then image overlay patterns for the adjacent upper and lower print lines become discontinuous at boundary portions, and consequently, image overlay patterns are not linked between the upper and lower print lines.